//! `notes.md`: experience, append-only. Each entry is a header line saying how it got there,
//! then its text (M5a spec, section 3):
//!
//! ```text
//! § noted 2026-09-24T21:02Z in session mm-dh45qg… · private · untrusted
//! § moved 2026-09-24T20:14Z from memory.md in session mm-y73sxj…
//! § dropped 2026-09-24T20:14Z from memory.md in session mm-y73sxj…
//! ```

use bxcore::{DataClass, MemoryFile, Timestamp};

/// How an entry came into `notes.md`.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Kind {
    /// Something seen or told, with the session's class and whether it had read untrusted
    /// content.
    Noted { class: DataClass, untrusted: bool },
    /// Identity that `consolidate` took out of the prompt: still held true.
    Moved(MemoryFile),
    /// Identity the agent stopped holding true.
    Dropped(MemoryFile),
}

/// One entry of `notes.md`.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Note {
    pub kind: Kind,
    /// `YYYY-MM-DDTHH:MMZ`.
    pub time: String,
    pub session: String,
    pub text: String,
}

/// A time as the notes show it: to the minute, in UTC.
pub fn minute(time: Timestamp) -> String {
    let s = time.to_rfc3339();
    format!("{}Z", s.get(..16).unwrap_or(&s))
}

fn class_name(class: DataClass) -> &'static str {
    match class {
        DataClass::Public => "public",
        DataClass::Private => "private",
        DataClass::Secret => "secret",
    }
}

fn file_of(name: &str) -> Option<MemoryFile> {
    match name {
        "memory.md" => Some(MemoryFile::Memory),
        "user.md" => Some(MemoryFile::User),
        _ => None,
    }
}

impl Note {
    /// The header line, without its newline.
    pub fn header(&self) -> String {
        match &self.kind {
            Kind::Noted { class, untrusted } => {
                let mut s = format!(
                    "§ noted {} in session {} · {}",
                    self.time,
                    self.session,
                    class_name(*class)
                );
                if *untrusted {
                    s.push_str(" · untrusted");
                }
                s
            }
            Kind::Moved(file) => {
                format!(
                    "§ moved {} from {} in session {}",
                    self.time,
                    file.name(),
                    self.session
                )
            }
            Kind::Dropped(file) => {
                format!(
                    "§ dropped {} from {} in session {}",
                    self.time,
                    file.name(),
                    self.session
                )
            }
        }
    }

    /// The header, the text and a final newline: what is appended to `notes.md`.
    pub fn render(&self) -> String {
        format!("{}\n{}\n", self.header(), self.text)
    }
}

/// Read a header line back, or `None` when the line is not one.
fn parse_header(line: &str) -> Option<(Kind, String, String)> {
    let after = line.strip_prefix("§ ")?;
    let (word, rest) = after.split_once(' ')?;
    let (time, rest) = rest.split_once(' ')?;
    match word {
        "noted" => {
            let rest = rest.strip_prefix("in session ")?;
            let parts: Vec<&str> = rest.split(" · ").collect();
            if parts.len() < 2 || parts.len() > 3 {
                return None;
            }
            let session = parts[0];
            if session.is_empty() || session.contains(' ') {
                return None;
            }
            let class = match parts[1] {
                "public" => DataClass::Public,
                "private" => DataClass::Private,
                "secret" => DataClass::Secret,
                _ => return None,
            };
            let untrusted = match parts.get(2) {
                None => false,
                Some(&"untrusted") => true,
                Some(_) => return None,
            };
            Some((
                Kind::Noted { class, untrusted },
                time.to_string(),
                session.to_string(),
            ))
        }
        "moved" | "dropped" => {
            let rest = rest.strip_prefix("from ")?;
            let (file_name, after) = rest.split_once(' ')?;
            let file = file_of(file_name)?;
            let after = after.strip_prefix("in session ")?;
            if after.is_empty() || after.contains(' ') {
                return None;
            }
            let kind = match word {
                "moved" => Kind::Moved(file),
                _ => Kind::Dropped(file),
            };
            Some((kind, time.to_string(), after.to_string()))
        }
        _ => None,
    }
}

/// The entries of `notes.md`. Text before the first header, or under a line that is not a
/// header, belongs to the entry above it; the owner may have edited the file.
pub fn parse(text: &str) -> Vec<Note> {
    let mut notes: Vec<Note> = Vec::new();
    for line in text.lines() {
        if let Some((kind, time, session)) = parse_header(line) {
            notes.push(Note {
                kind,
                time,
                session,
                text: String::new(),
            });
        } else if let Some(last) = notes.last_mut() {
            if last.text.is_empty() {
                last.text.push_str(line);
            } else {
                last.text.push('\n');
                last.text.push_str(line);
            }
        }
    }
    for note in &mut notes {
        note.text = note.text.trim().to_string();
    }
    notes
}